Reduction in size and weight is required for electric and electronic equipment such as personal computer, OA equipment, AV equipment, mobile phone, phone, facsimile, home appliance, and toys with the spread of mobile equipment. In addition to such requirements, the part constituting the equipment, and in particular, casing is required to satisfy the requirements of higher strength, higher rigidity, and thinner wall so that the casing is not largely deformed to become in contact with and induce breakage of the parts accommodated in the casing when a load is applied from its exterior.
Another property required for the casing of electronic equipment is the performance of suppressing electromagnetic interference (EMI) by shielding the radio wave, namely, the radio wave shielding performance. This property is required for preventing the effects on the operation of other equipment and human body by the radio wave emitted from the equipment during its operation. The electromagnetic wave emitted from the electronic equipment itself may adversely affect the operation of other equipment.
In addition, many of the notebook personal computers, mobile phones, and tablet products are equipped with an antenna for wireless communication, and inmost cases, such antenna is accommodated in the interior of the casing considering the portability and design convenience. When a material having a high electromagnetic wave shielding property, for example, a carbon fiber reinforced plastic or a metal such as magnesium alloy is selected for the material constituting the entire surface of the casing of such equipment, the casing having a high radio wave shielding performance invites functional problem of deteriorated radio communication performance due to decrease in average antenna gain, biased radio wave directivity, and the like.
In addition, in the case of products accommodating radio communication function having increased functionality in its interior, the product is required to have a reduced size, and the heat generated from the parts accommodated in the interior has considerable effects and dissipation of the heat is an important task.
Patent Document 1 discloses the technology of improving strength of the junction part and mass productivity while retaining the radio wave shielding property without detracting from the radio communication performance by integrating a casing for electronic equipment having a radio wave shielding material comprising a fiber-reinforced resin and a radio wave permeating member comprising fiber reinforced thermoplastic resin comprising a thermoplastic resin having a certain amount of non-conductive reinforcing fiber added thereto by a method wherein thermoplastic resin adhesion layer is placed in the adhesion interface between the radio wave shielding material and the radio wave permeating member so the thermoplastic resin adhesion layer will be present on the adhesion interface of the radio wave shielding material and the radio wave permeating member by means of outsert injection molding.
However, in the technology disclosed in Patent Document 1, thickness of the radio wave shielding member that is set first does not change before and after the molding, and adjustment to match the thickness of the 2 materials, namely, the radio wave shielding member and the radio wave permeating member in the molding is difficult. Accordingly, a step is generated along the junction of the resulting molded article, and for example, a line of junction is visually recognizable even after the coating of the molded article adversely affecting the design property of the article. In addition, in the Patent Document 1, the radio wave permeating member used in the radio wave permeable area for realizing the radio communication performance is an insulating material, and since an insulating material generally suffer from the high press shrinkage, provision of a large radio wave permeable area may invite the problem of warping and deformation of the casing after the injection molding due to the difference in the molding shrinkage.
Patent Document 2 discloses the technology of particularly improving design property while retaining the radio wave shielding property without detracting from the radio communication performance by forming a molded article of a fiber reinforced plastic by preparing a sheet-shape molding precursor comprising a molding material substrate (A) containing a conductive fiber as the reinforcing fiber and a thermoplastic resin as the matrix and a molding material substrate (B) containing an insulating fiber as the reinforcing fiber and a thermoplastic resin as the matrix, wherein the molding material substrate (B) is inserted through the molding material substrate (A) in the thickness direction to forma sheet-shape molding precursor; heating the molding precursor to a temperature higher than the melting temperature of the thermoplastic resin; and thereafter conducting the press molding at a temperature lower than the melting temperature of the thermoplastic resin to form a molded article of the fiber reinforced plastic.
However, the technology disclosed in Patent Document 2 require preliminary cutting of the part where the radio wave permeable area is to be formed in the molding material substrate (A), and also, preliminary preparation of the molding material substrate (B) which should have a shape in precise size conformity with the cut portion in the molding material substrate (A). Accordingly, despite the capability of producing the casing having the radio wave permeable area by partial use of the insulating substrate, the production process is complicated with the unsolved problem of the production cost.
Patent Document 3 discloses the technology of producing a composite laminate plate having an improved design property with partial radio wave permeable area while retaining the electromagnetic wave shielding property without detracting from the radio communication performance by forming a pre-molding laminate of two or more composite substrates each prepared by abutting and joining a first reinforcing substrate which is a sheet paper having conductive discontinuous reinforcing fibers and a second substrate which is different from the first substrate wherein a matrix resin sheet containing a thermoplastic resin as its main component is disposed at least in some parts between the layers of the substrate laminate; placing the pre-molding laminate in a pair of mold; thermally melting the pre-molding laminate by applying pressure to the mold by a pressing machine to impregnate the matrix resin which had been in sheet form into the pre-molding laminate; and then cooling and shaping the laminate in the mold for integral molding.
However, in the technology disclosed in Patent Document 3, while retention of the electromagnetic wave shielding property without sacrificing the radio communication performance is enabled by abutting and joining an electromagnetic wave shielding member having a high radio wave shielding performance and a radio wave permeable member having a low radio wave shielding performance, there is yet room for improvement in the strength of the abutting joint between the electromagnetic wave shielding member and the radio wave permeable member, and there is also yet room for improvement in the flexibility for enabling diversification of the product since the shape of the electromagnetic wave shielding member and the radio wave permeable member had to be changed depending on the position of the radio wave generator member in the electronic equipment casing.